Optical mark scanning apparatus (often referred to as optical mark reading or OMR systems) and the scannable forms for such systems are well known in the prior art. There are a wide variety of applications that use OMR systems and scannable forms in the large-scale gathering of information (e.g., standardized tests, census information, preference surveys, etc.). The scannable forms for use in such systems are sheets of paper or other similar material that typically have a timing track comprised of plurality of pre-printed scan control marks (sometimes referred to as timing marks) in a control mark column and a plurality of response areas consisting generally of a row of response bubbles located on the sheet in a specified relationship with the scan control marks. The scan control marks are used to trigger the OMR system to scan or "read" the response areas associated with that scan control mark to detect whether a data mark is present at a particular response bubble. Scan control marks may also be used to indicate the beginning or end of the scanning operation for a scannable form.
Most OMR systems utilize a scannable form with a single timing track comprising a control mark column of identically spaced, uniform scan control marks (e.g., U.S. Pat. No. 3,831,009). Other prior art OMR systems use either one or two timing tracks comprising a control mark column having mostly uniform scan control marks with a first and/or last scan control mark of a different size or shape to indicate control functions other than scan or read, such as start scanning a form or stop scanning a form (e.g., U.S. Pat. Nos. 3,793,472 and 3,900,961). Still other prior art systems use more than one type of scan control mark to signal the scan or read (e.g., U.S. Pat. No. 3,886,326).
The ability to encode data information on the scannable form has long been recognized as desirable. For purposes of the present invention, data information is defined as information that is known or determined prior to the respondent completing the scannable form (e.g., school, class, grade, correct answer, etc.). For example, U.S. Pat. No. 3,643,348 describes a scannable form having the test answers encoded in a set of columns adjacent the control mark column so that the forms may be scored without the need of a separate answer key. Other forms have utilized separate pre-printed or pre-encoded response areas to designate data information on the scannable form before the respondent completes the form. One example of this approach is the use of bar codes or bar code stickers affixed to the form to convey the data information.
Unfortunately, such prior art schemes utilize valuable space on the scannable form and may be aesthetically undesirable in certain applications or require additional circuitry to decode the data information. The traditional method of using a data mark positioned in one response bubble among a group of response bubbles is an inefficient means for encoding data information that is known prior to the respondent completing the form. For example, a typical name field on a scannable form to be completed by a respondent might use a plurality of columns of letters to represent the letters of the respondent's name, each column having 26 response bubbles corresponding to the 26 letters of the alphabet. Obviously, this method of encoding data information wastes space on the scannable form and requires additional processing in order to decode the information into a form usable by a data processing system. On the other hand, while the bar code method minimzes the space on the scannable form necessary to encode the data information, it requires the use of additional hardware circuitry in order to properly decode the data information encoded in the bar codes.
Although the existing scannable forms may be satisfactory for situations where no data information is to be pre-encoded on the scannable form or where only a relatively small amount of data information is to be pre-encoded, they are not well-suited for pre-encoding significant amounts of data information on a scannable form. Accordingly, there is a continuing need for improvements in scannable forms for OMR systems to allow for the pre-encoding of data information in a manner that maximizes the amount of data information that may be encoded in a minimum amount of space on the scannable form without interfering with other areas on the scannable form. Such a scannable form should provide for an efficient coding and retrieval of the pre-encoded data information, yet be both cost-effective and consistent with current OMR systems standards.